The present invention relates to filtering separators in particular pocket or tube filters, of the kind in which smoke-laden gas containing dust particles of particularly great adhesiveness is fed into a dust-collecting trough of a filter housing located at the bottom of the filter housing and then flows upwards towards filter elements, and in which said filter elements are cleaned periodically by counter-current scavenging and/or joggling, A portion of the setting dust agglomerated in said filter which corresponds to the amount of dust in the incoming smoke-laden gas and which cannot be carried back to the filter surfaces by the smoke-laden gas is removed from said dust-collecting trough. Hereinafter such apparatus will be referred to as "of the kind described".
With a filtering dust separator of the kind described it is possible, such as disclosed for example in U.S. Pat. No. 4,140,502 of the present inventor, by means of a continual feedback to the filter surfaces of the dust which settles when the filter surfaces are cleaned periodically, to bring about an agglomeration of the fine dust contained in the smoke-laden gas while it is in a floating state and downstream of the filter surfaces of the filter elements, which agglomeration increases steadily until the incoming smoke-laden gas is no longer capable of feeding further quantities of dust back to the filter surfaces, so that large agglomerated dust particles sink down through the layer of smoke-laden gas into the dust collecting trough and are removed therefrom by a screw or the like. This amount of dust corresponds to the amount of dust in the smoke-laden gas flowing into the filter. As a result of the agglomeration of the fine dust which occurs, the permeability of the layer of dust on the filter surfaces facing the smoke-laden gas is maintained until the periodic cleaning of the filter surfaces becomes necessary, and above all this makes it possible for the filter surfaces to be cleaned by counter-current scavenging and/or joggling, since very fine dust particles are prevented from remaining clinging to the filter surfaces by the agglomeration.
The above-mentioned method has proved satisfactory in practice. However, under certain circumstances very fine dust particles from smoke-laden gases, in particular particles of great adhesiveness which build up on each other and on the filter surfaces, cling to the filter surfaces or, as is often the case, remain hanging on the individual fibres of the filter surfaces in small clumps when conventional cleaning processes are used, despite the agglomeration by means of the feedback of dust, and this may lead to irreversible clogging of the filter accompanied by a steady reduction in filtering speeds and a sharp rise in the resistance of the filter to flow, which means that the filter system would have to be enlarged to a size which would not be economically practicable.
It is an object of the invention, in filtering separators such as pocket or tube filters in which there is feedback of the dust from smoke-laden gases which is to be periodically freed from the filter surfaces and fed back to the filter surfaces, to store the said dust temporarily upstream of the filter elements and thus age and pre-agglomerate it, and at the same time to make use of the fact of storage to remove the excess dust particles which occur each time the filter surfaces are cleaned and which cannot be carried back to the filter elements in the smoke-laden gas.